Pull the carb and see what's in there now. Then go over to rockymtatvmc.com and get some jets. 2 pilots and 2 mains going the 2 next lower sizes that are in the bike now. Experiment with the needle position as well.

I've been at several altitudes with many different bikes. 8000' will not be too bad, even stock, most newer bikes are lean anyway. 10,000' and above is when it becomes an issue. I have been going to Colorado many years and the rule of thumb with 4 strokes has been go down 10% on the main and call it good, no messing with air/fuel screw or needles. So a 150 main would be replaced with a 135 and that has worked great for us on all our bikes. Some bikes and carbs like more or less and are more sensitive to changes, but overall 10% has been golden for us from 10,000' to 14,000'. There are other tricks that help in a pinch, we had ATV's one year and they liked it better with the cover of the air box removed above the tree line (12,500') but otherwise were OK. Pulling the snorkel of the air box may also help a little, but overall 10% has been fine for a week of trail riding. Hope that helps, I'd try the tricks listed above if it doesn't run well stock and have a 10% smaller main jet on hand just in case, but if you're not over 8,000' you'll probably be better off than you realize. We have brought everything from an XR80 to an XR650L and never had an issue with only swapping the main.

I've been at several altitudes with many different bikes. 8000' will not be too bad, even stock, most newer bikes are lean anyway. 10,000' and above is when it becomes an issue. I have been going to Colorado many years and the rule of thumb with 4 strokes has been go down 10% on the main and call it good, no messing with air/fuel screw or needles. So a 150 main would be replaced with a 135 and that has worked great for us on all our bikes. Some bikes and carbs like more or less and are more sensitive to changes, but overall 10% has been golden for us from 10,000' to 14,000'. There are other tricks that help in a pinch, we had ATV's one year and they liked it better with the cover of the air box removed above the tree line (12,500') but otherwise were OK. Pulling the snorkel of the air box may also help a little, but overall 10% has been fine for a week of trail riding. Hope that helps, I'd try the tricks listed above if it doesn't run well stock and have a 10% smaller main jet on hand just in case, but if you're not over 8,000' you'll probably be better off than you realize. We have brought everything from an XR80 to an XR650L and never had an issue with only swapping the main.